Archaeologists have been arguing for more than a century about whether people first entered the American continents before, during or after the coldest peak of the last ice age, called the Last Glacial Maximum (LGM). Now, a new study of the available genetic evidence suggests the group that gave rise to today's Indigenous people migrated to the Americas no earlier than 21,000 years ago.

"The evidence points to the arrival of humans ancestral to contemporary Indigenous peoples likely near the end of the Last Glacial Maximum, but earlier migrations may also have occurred," study co-authors Bethany Potter, an archaeologist at the Kansas Geological Survey, and Savannah Hay, a biological anthropologist at the University of Kansas, told Live Science in an email.

In a study published online Sept. 23 in the journal Current Opinion in Genetics & Development, the researchers used genetic evidence to investigate the three main archaeological models for Native American origins: an entry into the Americas before the LGM more than 25,000 years ago, entry during the LGM some time between 25,000 and 14,000 years ago, and entry after the LGM more recently than 14,000 years ago, sometimes called the Clovis First theory.

"The reason this topic is so contentious among anthropologists is because not all archaeologists agree about which of the earliest sites are legitimate, and that influences which model they think is most accurate," Potter and Hay said. "We know that humans were definitely in the Americas by about 13,500 years ago. We still don't know if they arrived earlier than that and, if so, how much earlier."

Genetic evidence of the first people in the Americas is scarce. The first whole genome from an ancient Indigenous person, who lived around 4,000 years ago in Greenland, was sequenced in 2010. Since then, the researchers wrote in the study, scientists have published around 250 whole genomes, along with genome-wide data from around 1,200 ancient Indigenous people.

These DNA studies have revealed key information about the first people in the Americas. During the LGM, around 25,000 years ago, a group of people living somewhere near Siberia or Beringia, which included the land bridge connecting Asia to Alaska, split into different groups ‪—‬ ancient Native Americans, ancient Beringians and one or more "ghost" lineages ‪—‬ and moved quickly along the Pacific coast, possibly splitting again around 16,000 years ago into Northern Native Americans and Southern Native Americans.

"Huge gaps in our genetic dataset"

Although the current genetic data lines up with archaeological evidence of people entering the American continents at least 14,000 years ago and perhaps as far back as 21,000 years ago, more DNA evidence is needed to fully understand how and when the first Indigenous people arrived from Siberia.

"There are huge gaps in our genetic dataset," Potter and Hay said. "For example, there are still no published ancient genomes from the Great Plains, despite that being where our lab group is situated." And these gaps could be hiding evidence of earlier migrations.

Human footprints found at White Sands, an archaeological site in New Mexico, have been dated to 23,000 years ago. If this date is correct, it implies that people were living there prior to the LGM. The Acoma Pueblo people living in the region of White Sands today recognize these footprints as traces of their ancestors, Potter and Hay said.

But genetic data from contemporary and ancient Indigenous peoples in the Americas currently shows that the White Sands population did not make a significant genetic contribution to the ancestors of today's Indigenous people, the researchers said. "However, it is possible we have not sampled their descendants' lineage, or that they contributed a low proportion of genetic ancestry to ancient North American populations," they said. "Perhaps we've just not found DNA from the White Sands population yet."

There are several scenarios compatible with a pre-LGM entry of people into the Americas, the researchers wrote, but assessing those models also requires more genetic data. To date, the earliest sampled genome is from a 12,800-year-old individual known as the Anzick-1 child, whose bones were found in Montana. Extrapolation from the DNA of the Anzick child and other early ancestors points to an initial migration that occurred no earlier than 21,000 years ago, Potter and Hay said.

"Expanding geographic coverage in general would be hugely beneficial, but many of us are intentionally slow with our ancient DNA approaches to ensure research relevant to descendant communities is ethical and collaborative," Potter and Hay said.

It is unclear when or if the longstanding question of when people first entered the Americas will be resolved, as current archaeological and genetic evidence do not unequivocally point to a single answer, Potter and Hay said, but "the publication of new ancient genomic data from the Americas is powerful, as it has the potential to fill in these gaps and reframe how we see these early peopling events."

How much do you know about the first people to reach the Americas? Find out with our First Americans quiz!